1. Field of the Invention
The present invention relates to an image forming apparatus represented by a copier or a printer.
2. Description of the Related Art
An image forming apparatus such as a copier or a printer generally includes a sheet feeding section in which sheets before printing are accommodated in a stacked manner; a sheet conveying section for conveying a sheet from the sheet feeding section to a transfer unit; an image forming unit for forming a toner image; the transfer unit for transferring the toner image to the sheet; and a fixing unit for fixing the unfixed toner image to the sheet. Some of image forming apparatuses include a plurality of sheet cassettes as a sheet feeding section in a bottom part of a main body of the image forming apparatus and include an image forming unit, a transfer unit and the like in an upper part in order to minimize an installation floor area.
A sheet conveying section for conveying a sheet from the sheet cassette in the bottom part of the apparatus main body to the transfer unit and the like in the upper part is, in many cases, formed to vertically extend along a side surface of the main body for the miniaturization of the image forming apparatus, thereby forming a vertical conveyance path. Here, a manual sheet feeding section is used in the case of using sheets such as thick paper sheets or OHP sheets wished to be fed into the image forming apparatus one by one without using the sheet cassette. In order to suppress a curvature of a sheet conveyance path, the manual sheet feeding section is sometimes disposed at a side surface of the main body opposite to the one where the vertical conveyance path is formed. One example of such an image forming apparatus can be found in Japanese Unexamined Patent Publication No. 2003-131483 (document D1).
On the other hand, since the image forming unit performs an image forming operation while conveying a sheet, many conveyance rollers as conveying members for conveying the sheet and many rotary members relating to the image formation such as a photoconductive drum, a developing roller, a cleaning roller and a fixing roller are disposed at various positions. Particularly in an image forming apparatus for color printing, a plurality of image forming units are constructed due to the necessity to form toner images of different colors, which further increases the number of rotary members relating to the image formation.
The image forming apparatus is provided with a plurality of driving mechanisms for rotating these rollers and rotary members. The driving mechanisms include driving sources and power transmitting members such as motors, gears, belts and clutches. Such driving mechanisms are unitized in view of recyclability, assemblability and maintainability in some cases. One example of an image forming apparatus in which driving mechanisms for image forming units are unitized can be found in Japanese Unexamined Patent Publication No. 2005-91780 (document D2).
The image forming apparatus disclosed in document D2 is a so-called tandem-type image forming apparatus provided with four image forming units for forming toner images of different colors and an intermediate transfer belt, and the driving mechanisms for the image forming units at four positions and the intermediate transfer belt are unitized. In view of parts cost and space to be taken up upon constructing such a driving mechanism, it is desirable to rotate as many rollers and rotary members as possible by the driving mechanism constructed by a minimum number of parts.
Further, in the case of having the manual sheet feeding section at the side surface of the main body opposite to the one where the main vertical conveyance path is formed as in the image forming apparatus disclosed in document D1, the power transmitting members have to be constructed such that power can be transmitted to parts relatively distant from the driving source. This results in lower assemblability and maintainability and increases a power transmission loss to decrease driving efficiency. Accordingly, in an image forming apparatus provided with many rollers and rotary members, it is preferable to design driving mechanisms for driving the rollers and rotary members with suitable efficiency while promoting lower costs and miniaturization.